The proposed research will develop a comparative primate model to study the effects of stress on immune responses. Although it is generally acknowledged that stress can compromise resistance to disease, further research is still needed to determine how different types of stress influence specific aspects of immune responses. In addition, better animal models are needed in this field because of marked species differences and the difficulties inherent in generating stress paradigms that are comparable to human situations. We propose to study two primate species, the squirrel monkey and the rhesus monkey, because they offer two dramatically different physiological systems for evaluating the relationship between psychoendocrine activation and immune responses. The endocrinological and immunological consequences of a non-invasive stress occurring under natural circumstances will be investigated. For the young infant and lactating female, we propose to utilize the varying degrees of stress that can be reliably evoked by different types of mother-infant separation. In the adult, we propose to evaluate the effects of disturbances in ongoing social relations: the response to isolation, the xenophobic response to unfamiliar conspecifics, and the agitation involved in establishing new social relations. Stress will be assessed by measuring changes in circulating levels of plasma cortisol and by alterations in behavior. Immune competence will be measured in control and stressed individuals by measuring (1) immunoglobulin levels; (2) antibody response to specific challenge; (3) level of hemolytic complement (CH50) as well as complement components C4 and C3; (4) macrophage function as indicated by chemiluminescence; (5) T cell function as indicated by measurement of 'active' response to mitogen stimulation and inducibility of specific T cell responsiveness to antigen stimulation; (6) natural killer cell activity.